The present invention generally relates to an atrial cardioverter having a system for detecting atrial tachyarrhythmias of a heart. The present invention is more particularly directed to such a system and method which detects atrial tachyarrhythmias with a high degree of specificity even though the heart may be paced at the same time in a dual or single chamber mode.
Atrial tachyarrhythmias are common cardiac arrhythmias and are evidenced by very fast atrial rates. They are generally classified as either atrial flutter which is also generally associated with a fast and substantially constant ventricular rate or atrial fibrillation which is also generally associated with a fast but variable ventricular rate.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life-threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. Because patients afflicted with atrial fibrillation generally experience rapid and irregular beating of the heart they may even experience dizziness as a result of reduced cardiac output.
Atrial tachyarrhythmia occurs suddenly, and many times can only be corrected by discharging electrical energy into the atria of the heart of the patient. This treatment is preferably synchronized to a detected R wave of the heart in order to avoid shocking the atria during the T wave or vulnerable period of the heart. The amount of energy which may be required to successfully cardiovert the atria can be as low as one joule and as high as six joules. In the cases of atrial fibrillation, energy of about two to six joules is often effective to cardiovert atrial fibrillation back to normal sinus rhythm (NSR).
Implantable atrial cardioverters or defibrillators are known which detect the presence of an atrial tachyarrhythmia and provide a single cardioverting pulse of electrical energy to the atria when atrial fibrillation is detected. Atrial tachyarrhythmia detection may be initiated at spaced apart times with such devices to conserve battery power as disclosed, for example, in U.S. Pat. No. 5,464,432. Alternatively, such devices may provide continuous monitoring of heart activity to activate more specific atrial tachyarrhythmia detections when the monitored activity indicates a probability of an atrial tachyarrhythmia.
One such implantable device is disclosed in U.S. Pat. No. 5,282,837. As disclosed in that patent, ventricular activity is continuously monitored. When the ventricular rate and/or ventricular rate variability reach a certain level, an atrial tachyarrhythmia is suspected and a more robust and higher battery energy consumption algorithm for atrial fibrillation detection is initiated and implemented with a microprocessor.
Whether continuous monitoring or intermittent monitoring is used to initiate atrial tachyarrhythmia detection, such detection must be highly specific to an atrial tachyarrhythmia. The reason for this is that patients will normally be conscious during the atrial tachyarrhythmia therapy. While highly specific atrial tachyarrhythmia detection algorithms are known, these algorithms have not been called upon to detect atrial tachyarrhythmias in the presence of single or dual chamber pacing. Such pacing from an atrial cardioverter or defibrillator has recently received great attention and support as a way to adapt an atrial cardioverter/defibrillator for a greater number of patients.
The present invention provides such specific atrial tachyarrhythmia detecting notwithstanding the presence of single or dual chamber pacing. More specifically, the present invention first relies upon atrial activity sensing within the right atrium to reduce far field sensing as much as possible. Further, detection windows are established whereby only heart activity free of any heart activity other than spontaneous atrial heart activity is relied upon in detecting an atrial tachyarrhythmia.